import {reactive, ref, toRefs, toRef, computed, 
    watch,watchEffect,watchPostEffect,
  defineExpose, defineProps,withDefaults,
  onBeforeMount,onMounted,onBeforeUpdate,onUpdated,
  onBeforeUnmount,
  onUnmounted
} from 'vue'

 
export default function useSum() {
    let sum = ref(0)

    const add = () => {
      sum.value++
    }

    return {
      sum,
      add
    }
}
